Cannot login to MYOB after clearing API tokens

There appears to be a change in behaviour in the API file connection process today.

Using our add-in report-writer program, if we retain existing tokens, then connect, all is well. 

But if we clear the API tokens (access & refresh) for that company, then try to create the connection again, the login window prompts for an email address, but after that no password prompt appears. Therefore our add-on program loses access to that file.

The normal MYOB file login process is working without error.